Surface treatment of magnesium and magnesium base alloys



252. COMPOSITIONS.

Patented June 23, 1942 UNITED STATES PATENT OFFICE SURFACE TREATMENT OFMAGNESIUll/I AND MAGNESIUM BASE ALLOYS No Drawing.

Application July 8, 1941,

Serial N 0. 401,463

6 Claims.

This invention relates to the cleaning of magnesium articles and is moreparticularly con cerned with the production of bright surfaces uponarticles of that metal and its alloys.

The term magnesium as used in this specification and in the appendedclaims includes not only magnesium itself but also the so-called manesium base alloys containing more than 70 per cent magnesium.

During the working of magnesium and its alloys, the metal usuallybecomes coated with foreign matter, such as the lubricant used duringthe working operation and various other impurities, which may even beembedded in the surface of the metal itself. This foreignmatterusuallymay be removed by etcfiing'the' surface of the worlg piece'in any ofseveral chemicalsolutions, gie most generally used 'arwfireh sraque'ams'omli nfia qlltaining sulfuric gem, These chemical treatments, however,are not entirely satisfactory. One of their chief disadvantages is that,while they remove foreign matter and clean the surface of the metal in asatisfactory manner, they generally accompany the cleaning of thesurface with a dull rough etch. This necessitates a subsequent operationif the surface of the metal is to be smoothed and brightened.

An object of this invention, then, is to provide an improved method forcleaning articles of magnesium. A more particular object is to devisesuch a method which also provides the magnesium work piece with a brightshiny surface.

The specific object of this invention is to provide a method wherebysurfaces of magnesium objects may be treated in an aqueous cleaningsolution containing sulfuric a gid to remove lubricants and otherforeigfffiiatter, with which the surface of the metal has becomecontaminated during a working or similar operation, and at the same timebe rendered bright and shiny.

My invention is predicated upon the discovery that if the aqueoussulfuric acid solutions heretofore used for cleaning magnesium surfacesalso contain certain soluble organic aromatic compounds, the action ofthese cleaning solutions upon the magnesium becomes modified and, instead of leaving the magnesium surface dull and rough, the cleaningaction of the solutions upon the metal is accompanied by a brighteningeffect which leaves the metal uniformly bright and shiny.

The soluble additive substances which are used with sulfuric acid tomodify the action of the cleaning solution in accordance with my invention are the soluble organic compounds comprising the group consistingof phenol, resorcinoq mgrogallgl and gallic acid. These substances arebehave like these other organic compounds. Also,

I have found that the organic content used to modify the action of thesolution need not be restricted to a single one of these compounds 'butmay consist of mixtures of these substances. While it is preferable touse these aromatic compounds, it is possible to substitute their salts,such as their alkali metal and ammonium salts, since such salts formthese free aromatic compounds in the aqueous sulfuric acid solution.

The total amount of these aromatic additive compounds in the. solutionmay range from about 0.5 per cent to about 15 per cent by weight, but ispreferably maintained between about 3 per cent and 5 per cent. Suchamounts of these aromatic compounds in aqueous solutions containingbetween about 1 and 10 per cent, and preferably between about 2 and 6per cent by weight sulfuric acid cause the surface of magnesium, whichbecomes dull when cleaned in the known sulfuric acid solutions, tobecome not only freed of any foreign matter but also bright and shiny.The balance of the cleaning solution is substantially all water. By thisI mean that the balance of the solution, while it may contain magnesiumsulfate and other reaction products produced during the cleaningoperation and minor amounts of other substances which do not interferewith the cleaning and brightening action of the sulfuric acid and thearomatic additive compounds, is essentially aqueous. This aqueoussolution also may contain one or more of the aliphatic polybasic acidsfrom the group consisting of oxalic, malic, citric, and tartaric acidswhich comprise another group of substances which are in many respectssimilar to these aliphatic additive compounds and are more fullydescribed in my copending application, Serial No. 401,464, filed July 8,1941. The presence of these aliphatic dibasic acids, however, is notnecessary since they do not appear to influence the cleaning andbrightening effect of the solution.

These aromatic additive compounds do not appear to interfere with thecleaning action of the sulfuric acid to any substantial extent. Theirfunction seems to be restricted almost entirely to modifying the actionof the solution in such a way that the magnesium work piece becomesbright and shiny during the cleaning step. It seems likely, however,that the phenolic compounds in the solution serve to retard slightly theattack of the sulfuric acid and to make its action more uniform. This isnot objectionable; in fact, it may be desirable, since the retarded anduniform attack of the acid prevents wedge effect, i. e. theprogressively diminishing cross section sometimes produced uponelongated articles of magnesium when the acid attack is greater upon somparts of the article immersed in the solution than upon other parts.

Preferably the solution should be maintained at about room temperatureduring the cleaning operation. Higher temperatures may also be employed;and use of the cleaning solution at higher temperatures may be desirablein some cases, since then smaller amounts of the active agents generallyare needed, and the cleaning and brightening step may be accelerated byheating the solution. However, the more rapid action at elevatedtemperatures may result in the presence of a greater amount of acidspray, and therefore be objectionable.

By the treatment of magnesium articles in accordance with my invention,hydrocarbons, such as lubricating oil, and other foreign matter areremoved from the surface of the work piece. The cleaning solution alsoattacks the surface of the metal itself and dissolves away any oxide andother magnesium compounds which may have formed upon the surface; and inaddition, the solution dissolves a minute but uniform layer of magnesiumfrom the surface of the work piece and thereby removes any impuritieswhich may be embedded in the surface of the metal. By treatment ofmagnesium work pieces as described herein, the magnesium surface is notonly cleaned of its impurities but also is left bright and shiny.

' The bright and shiny surface thereby provided usually is smooth andmirror-like; but in some instances when certain alloys are treated, thesurface, While still bright and shiny, may be slightly but uniformlyroughened.

Because of its capacity for removing foreign substances and oxide andfor dissolving embedded matter from magnesium surfaces, the process ofmy invention is especially adapted for the treatment of magnesiumarticles which have become coated with lubricants and various surfaceimpurities and into which foreign matter has become embedded duringworking operations. However, the use of my process is not restricted tomaterial which has been previously worked and it also may be used tobrighten the surfaces of magnesium articles which have already beencleaned by other operations.

The following examples'are given by way of illustration to show theoperation of my cleaning and brightening process:

Example 1 A specimen of a magnesium base alloy nominally containing 4.0per cent aluminum and .3 per cent manganese was cut from a sheet of thealloy as it came from a rolling operation, and, without being cleaned oflubricant and other foreign impurities, was immersed for 3 minutes atroom temperature in 100 cc. of an aqueous solution containing 3 per centby weight sulfuric acid and 3 per cent phenol. Upon removal from thesolution, the specimen was found to have been cleaned of its coating oflubricant and other foreign material, and to have a uniformly brightshiny surface.

Emample 2 A test specimen similar to that described in Example 1, and.of the same alloy, was treated at room temperature for 5 minutes in anaqueous solution containing 3 per cent sulfuric acid and 0.5 per centpyrogallol. By this treatment, the lubricant and other foreign matterwere removed and the surface of the specimen was left very smooth andbright.

Example 3 A specimen taken from a rolled sheet of commercially puremagnesium was immersed in an aqueous solution containing 3 per centsulfuric acid and 3 per cent resorcinol at a temperature of about 30 C.At the end of about 3 minutes the surface of the specimen was found tobe free from foreign matter and to be mirror bright.

Example 4 A panel taken from a rolled sheet of commercially puremagnesium was immersed at room temperature for 1 minute in an aqueoussolution containing 3 per cent sulfuric acid and 1 per cent gallic acid.The panel was thereby cleaned of all foreign matter and its surface leftsmooth and mirror bright.

Example 5 Following immersion for 3 minutes of a rolled specimen of amagnesium base alloy containing 4.0 per cent aluminum and 0.3 per centmanganese in an aqueous solution containing 3 per cent sulfuric acid, 1per cent,phenol, and 2 per cent resorcinol, the specimen was found tohave been cleaned of foreign matter and to have a smooth bright surface.

Example 6 A specimen taken from a rolled sheet of commercially puremagnesium was immersed in an aqueous solution containing 3 per centsulfuric acid, 1 per cent phenol, 2 per cent resorcinol, and 1 per centpyrogallol at about room temperature. After treatment in this solutionfor about 3 minutes, the surface of the specimen was found to be freefrom foreign matter and to be exceptionally bright and shiny.

These examples are given to indicate the compositions and methods ofoperating the solutions used in the practice of my invention, and itwill be understood that variations in its practice are possible withinthe scope of the appended claims.

I claim:

1. The method of cleaning magnesium articles which comprises subjectingsaid articles to the action of an aqueous solution containing from about1 to about 10 per cent sulfuric acid and a total of from about 0.5 toabout 15 per cent of at least one soluble aromatic compound selectedfrom the group consisting of phenol, resorcinol, pyrogallol, and gallicacid.

2. The method of cleaning magnesium articles which comprises subjectingsaid articles to the action of an aqueous solution containing from about2 to about 6 per cent sulfuric acid and a total of from about 3 to about5 per cent of at least one soluble aromatic compound selected from thegroup consisting of phenol, resorcinol, pyrogallol, and gallic acid.

3. The method of treating wrought magnesium articles in order to removelubricants and other r52. COMPOSITIONS.

impurities therefrom and to produce a bright shiny surface thereupon,which method comprises subjecting said articles to the action of anaqueous solution containing from about 1 to about 10 per cent sulfuricacid and a total of from about 0.5 to about 15 per cent of at least onesoluble aromatic compound selected from the group consisting of phenol,resorcinol, pyrogallol, and gallic acid.

4. The method of cleaning magnesium articles and producing a brightshiny surface thereupon which comprises subjecting said articles to theaction of an aqueous solution containing from about 1 to about 10 percent sulfuric acid and from about 0.5 to about 15 per cent phenol.

Examin;

5. The method of cleaning magnesium articles and producing a brightshiny surface thereupon which comprises subjecting said articles to theaction of an aqueous solution containing from about 1 to about 10 percent sulfuric acid and from about 0.5 to about 15 per cent resorcinol.

6. The method of cleaning magnesium articles and producing a brightshiny surface thereupon which comprises subjecting said articles to theaction of an aqueous solution containing from about 1 to about 10 percent sulfuric acid and from about 0.5 to about 15 per cent pyrogallol.

MIKE A. MILLER.

